Chemical sensors are widely used to sense one or more chemicals. The chemicals can be a solid, liquid and/or gas and/or one or more constituents and/or combinations thereof. The constituent can include an inorganic molecule, an organic molecule, compounds thereof and/or combinations thereof, and may be detected using one or more activators, such as an enzyme. Chemical sensors are widely used, for example in chemical analytics and/or as process controls in various fields, such as biotechnology, environmental protection and/or health care. For example, chemical sensors used in medical diagnostic or evaluation procedures often use electrochemical detection of an analyte provided by dry or fluid/liquid chemistries/electrolytes.
As is well known to those having skill in the art, a chemical sensor may employ one or more interdigitated electrodes that include a plurality of spaced apart interdigitated fingers. See, for example, U.S. Pat. No. 5,670,731 to Hintsche et al. entitled Electrochemical Sensor, and published PCT Application WO 97/34140 to Hintsche, entitled Detection of Molecules and Molecule Complexes. In sensors that use interdigitated electrodes, it may be desirable to have a small spacing between the fingers thereof, so as to allow small diffusion lengths for electrochemically active species, and thereby allow increased sensitivity of the sensor to small concentrations and/or small changes in concentration.
Unfortunately, in order to provide the small spacings between fingers of interdigitated electrodes, microelectronic processing methods may need to be used. See, for example, Niwa et al., Fabrication and Characteristics of Vertically Separated Interdigitated Array Electrodes, J. Electroanal. Chem., Vol. 267, 1989, pp. 291-297; Aoki, Theory of the Steady-State Current of a Redox Couple at Interdigitated Array Electrodes of Which Pairs are Insulated Electrically by Steps, J. Electroanal. Chem., Vol. 270, 1989, pp. 35-41; Aoki, Quantitative Analysis of Reversible Diffusion-Controlled Currents of Redox Soluble Species at Interdigitated Array Electrodes Under Steady-State Conditions, J. Electroanal. Chem., Vol. 256 1988, pp. 269-282; and Horiuchi et al., Limiting Current Enhancement by Self-Induced Redox Cycling on a Micro-Macro Twin Electrode, J. Electrochem. Soc., Vol. 138, No. 12, December 1991, pp. 3549-3553. These microelectronic processing methods may employ relatively high cost microelectronic substrates, such as silicon wafers, and/or relatively complex and/or expensive fabrication processes, such as high resolution lithography, to achieve the desired spacing. The chemical sensors that are produced thereby may be too expensive for some intended uses. For example, it may be desirable to provide a low cost, single-use disposable sensor that can be used as a drug abuse monitor for sensing small concentrations of drugs in urine and/or other biological samples.